Light extraction film with nanoparticle coatings

ABSTRACT

A multifunctional optical film for enhancing light extraction includes a flexible substrate, a structured layer having nanoparticles of different sizes, and a backfill layer. The structured layer effectively uses microreplicated diffractive or scattering nanostructures located near enough to the light generation region to enable extraction of an evanescent wave from an organic light emitting diode (OLED) device. The backfill layer has a material having an index of refraction different from the index of refraction of the structured layer. The backfill layer also provides a planarizing layer over the structured layer in order to conform the light extraction film to a layer of an OLED display device. The film may have additional layers added to or incorporated within it to an emissive surface in order to effect additional functionalities beyond improvement of light extraction efficiency.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 12/336,889, filedDec. 17, 2008, now allowed, the disclosure of which is incorporated byreference in its entirety herein.

BACKGROUND

Organic Light Emitting Diodes (OLEDs) are the basis for a new displayand lighting technology, providing a good match for high resolution orhigh pixel count high definition display applications, and forefficient, broad area, flexible lighting applications. OLED devicesinclude a thin film of electroluminescent organic material sandwichedbetween a cathode and an anode, with one or both of these electrodesbeing a transparent conductor. When a voltage is applied across thedevice, electrons and holes are injected from their respectiveelectrodes and recombine in the electroluminescent organic materialthrough the intermediate formation of emissive excitons.

In OLED devices, over 70% of the generated light is typically lost dueto processes within the device structure. The trapping of light at theinterfaces between the higher index organic and Indium Tin Oxide (ITO)layers and the lower index substrate layers is the major cause of thispoor extraction efficiency. Only a relatively small amount of theemitted light emerges through the transparent electrode as “useful”light. The majority of the light undergoes internal reflections, whichresult in its being emitted from the edge of the device or trappedwithin the device and eventually being lost to absorption within thedevice after making repeated passes.

Efforts have been made to improve the internal quantum efficiency(number of photons generated per electron injected) of OLEDs by meanssuch as modifying the charge injection or transport layers, usingfluorescent dyes or phosphorescent materials, or by using multilayerstructures (see, for example, K. Meerholz, Adv. Funct. Materials v. 11,no. 4, p 251 (2001)). Light extraction efficiency (number of photonsemerging from the structure vs. the number generated internally) can beinfluenced by factors external to the emission layers themselves.

A bottom emitting OLED may be thought of as consisting of a corecontaining high index of refraction layers (organic layers for lightgeneration, carrier transport, injection or blocking, and, typically, atransparent conductive oxide layer) and a low index of refractionsubstrate material (typically glass, but could be a polymer film).Therefore light that is generated within the core may encounter two highindex to low index interfaces where it might undergo internalreflection. Light unable to escape the core as a result of encounter atthe first interface is confined to a waveguide mode, while light passingthrough that interface but unable to escape from the substrate as aresult of reflection at the substrate-to-air interface is confined to asubstrate mode. Similar optical losses occur due to interfaces in topemitting OLEDs.

Various solutions have been proposed to affect light reaching thesubstrate-to-air interface by disturbing that interface (e.g.,microlenses or roughened surfaces). Others have introduced scatteringelements into the substrate or into an adhesive (see Published PCTApplication No. WO2002037580A1 (Chou)), thereby interrupting thesubstrate modes to redirect that light out of the device. There haveeven been some preliminary attempts to disturb the core-to-substrateinterface by introducing scattering or diffractive elements at thisinterface. Detailed analysis has shown that scattering or diffractingstructures will be most effective in extraction light when located atthis interface (M. Fujita, et al.; Jpn. J. Appl. Phys. 44 (6A), pp.3669-77 (2005)). Scattering efficiency is maximized when the indexcontrast between the scattering or diffractive elements and the backfillmaterial is large and when the length scale of the index contrastvariations is comparable to the wavelength of the light (see, forexample, F. J. P. Schuurmans, et al.; Science 284 (5411), pp. 141-143(1999)).

Fabrication of defect-free OLED devices in contact with this lightextracting layer will require a smooth planar surface, so planarity ofthe top surface of a light extraction film is important. There has been,however, some work on corrugating the electrode structure in order tocouple light out of the OLED (M. Fujita, et al.; Jpn. J. Appl. Phys. 44(6A), pp. 3669-77 (2005)); the resultant effects on the electric fieldsin the device are expected to have deleterious effects. So great caremust be taken to not adversely affect the electrical operation of thedevice while disturbing this interface. Practical solutions to balancingthese conflicting issues have not yet been proposed.

Similar problems in external efficiency exist with inorganiclight-emitting diodes (LEDs), where the very high refractive indices ofthe active materials can severely limit the extraction of internallygenerated light. In these cases, there have been some attempts toutilize photonic crystal (PC) materials to improve the extractionefficiency (S. Fan, Phys. Rev. Letters v. 78, no. 17, p. 3294 (1997); H.Ichikawa, Appl. Phys. Letters V. 84, p. 457 (2004)). Similar reports onthe use of PCs in connection with OLED efficiency improvement have begunto appear (M. Fujita, Appl. Phys. Letters v. 85, p. 5769 (2004); Y. Lee,Appl. Phys. Letters v. 82, p. 3779 (2003)), but previously reportedresults have involved time-consuming and costly procedures which do notlend themselves incorporation into existing OLED fabrication processes.

Accordingly, a need exists for a product which can enhance lightextraction from OLED devices in a form which is compatible withfabrication processes for these devices.

SUMMARY

A multifunctional optical film for enhancing light extraction,consistent with the present invention, includes a flexible substrate, astructured layer, and a backfill layer. The structured layer ofextraction elements has a first index of refraction, and a substantialportion of the extraction elements are in optical communication with alight emitting region of a self-emissive light source when the opticalfilm is located against the self-emissive light source. The extractionelements include nanoparticles of different sizes. The backfill layerhas a material having a second index of refraction different from thefirst index of refraction, and the backfill layer forms a planarizinglayer over the extraction elements.

A method of making a multifunctional optical film for enhancing lightextraction, consistent with the present invention, includes coating alayer of a material having a first index of refraction onto a flexiblesubstrate. Nanostructured features of different sizes are imparted intothe organic material to create a nanostructured surface. The organicmaterial having the nanostructured features is cured. A backfill layeris then applied to the nanostructured surface to form a planarizinglayer on the nanostructured surface. The backfill layer comprises amaterial having a second index of refraction different from the firstindex of refraction. Alternatively, a thin layer of nanoparticles may bedistributed on the surface of the film and then overcoated with anessentially planarizing material of a different index.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated in and constitute a part ofthis specification and, together with the description, explain theadvantages and principles of the invention. In the drawings,

FIG. 1 is a diagram of a bottom emitting OLED display device with alight extraction film;

FIG. 2 is a diagram of a top emitting OLED display device with a lightextraction film;

FIG. 3 is a diagram illustrating spatially modulated OLEDs for a solidstate lighting element;

FIG. 4 is a diagram of an OLED backlight unit with a light extractionfilm;

FIG. 5 is a diagram illustrating OLEDs used as an LCD backlight unit;

FIGS. 6-9 are diagrams depicting possible spatial configurations ofextraction elements; and

FIGS. 10-14 are diagrams depicting possible surface configurations ofextraction elements.

DETAILED DESCRIPTION

Embodiments include methods to form light-extracting nanostructures, orother nanostructures, in a polymer replication process, a directdeposition of nanoparticles, or other processes to make a lightextraction film for OLED devices. The multifunctional film product can,in addition to enhancing light extraction, serve additional functionssuch as a substrate, encapsulant, barrier layer, filter, polarizer, orcolor converter and may be employed either during or after manufactureof an OLED device. The film construction is based upon photonic crystalstructures, or other nanostructures, for improved efficiency of lightextraction from the devices by modifying the interface between high andlow index layers within the device.

Elements of the invention include the provision of structures ofdimensions comparable to or less than the wavelength of the light to becontrolled, the provision of a material with contrasting index ofrefraction to fill in the areas surrounding the structures and also toplanarize the structure in order to present an essentially smoothsurface to come in contact with the OLED structure, and the location ofthis index-contrasting nanostructured layer within a small enoughdistance from the light-emitting region to be effective in extractingthe light that would otherwise be trapped in that region.

Light incident from a high index material onto an interface with a lowerindex medium will undergo total internal reflection (TIR) for allincidence angles greater than the critical angle θ_(C), defined byθ_(C)=sin⁻¹ (n₂/n₁), where n₁ and n₂ are the refractive indices of thehigh- and low index regions, respectively. The electromagnetic fieldassociated with this light reflected by TIR extends into the lower-indexregion in an evanescent standing wave, but the strength of this fielddiminishes exponentially with distance from the interface. Absorbing orscattering entities located within this evanescent zone, typically aboutone wavelength thick, can disrupt the TIR and cause the light to passthrough the interface. Therefore, it is preferable that thenanostructured index contrast layer be located within the evanescentzone if it is to be most effective in causing extraction of the lightfrom the emission region by scattering or diffraction. Alternatively,the nanostructured index contrast layer need only be in opticalcommunication with a light emitting region of the self-emissive lightsource when the optical film is located against the self-emissive lightsource. The term “optical communication” means that a significant orsubstantial portion of the generated optical field from the light sourceis capable of reaching the scattering particles or nanostructure.

Replication master tools can be fabricated with regular or randomstructures of the required average periodicity for light extraction, 200nanometers (nm)-2000 nm, over increasingly larger areas. Combining thistooling capability with microreplication processes such as continuouscast and cure (3C) enable the formation of the photonic crystalstructures, or other nanostructures, on the surface of a film substrate.Examples of a 3C process are described in the following patents, all ofwhich are incorporated herein by reference as if fully set forth: U.S.Pat. Nos. 4,374,077; 4,576,850; 5,175,030; 5,271,968; 5,558,740; and5,995,690.

The terms “nanostructure” or “nanostructures” refers to structureshaving at least one dimension (e.g., height, length, width, or diameter)of less than 2 microns and more preferably less than one micron.Nanostructure includes, but is not necessarily limited to, particles andengineered features. The particles and engineered features can have, forexample, a regular or irregular shape. Such particles are also referredto as nanoparticles.

The term “nanostructured” refers to a material or layer havingnanostructures.

The term “photonic crystal structures” refers to periodic orquasi-periodic optical nanostructures interspersed with a material ofsufficiently different index of refraction that will enable thestructure to produce gaps in the spectrum of allowed electromagneticmodes in the material.

The term “index” refers to index of refraction.

The term “backfill” refers to the material incorporated into astructure, and of a different index from the structure, to fill in voidsin the structure and planarize the structure.

The term “extraction elements” refers to any type and arrangement ofnanostructures enhancing light extraction from self-emissive lightsources. The extraction elements are preferably not contained within avolume distribution.

Bottom Emitting OLED Display Device

FIG. 1 illustrates a structure of bottom emitting OLED device 100 havinga light extraction film. A bottom emitting OLED device is defined as anOLED device emitting light through the substrate. Table 1 describes theexemplary elements of device 100 and the arrangement of those elements,as identified by the reference numbers provided in FIG. 1. Each layer ofdevice 100 can be coated on or otherwise applied to the underlyinglayer.

TABLE 1 Bottom Emitting OLED Device with Light Extraction Film Ref. No.Type of Element 102 electrode 1 104 organic layers 106 electrode 2 108high index structure 110 low index structure 112 optional barrier layer114 substrate 115 optional functional layers 116 light extraction film

The substrate 114 is composed of a material, substantially transparent(transmissive) to the desired emitted wavelengths, that providessufficient mechanical support and thermal stability for the device.Substrate 114 preferably comprises a flexible material. Examples ofsubstrate materials include the following: glass; flexible glass;polyethylene terephthalate (“PET”); polyethylene naphthalate (“PEN”); orother translucent or transparent materials. Substrate 114 can optionallyalso function as a barrier layer. Also, substrate 114 can optionallycontain dyes or particles, and it can be tentered or include prismaticstructures.

The optional barrier layer 112 effectively blocks or helps preventpermeation of oxygen and water to the layers of the device, particularlythe organic layers. Examples of barrier layers are described in U.S.Patent Application Publication Nos. 2006/0063015 (describing boron oxidelayers with inorganic barrier layers) and 2007/0020451 (describingdiamond-like glass (DLG) and diamond-like carbon (DLC)), both of whichare incorporated herein by reference as if fully set forth.

The electrodes 102 and 106 can be implemented with, for example,transparent conductive oxide (TCO) such as indium tin oxide (ITO) ormetals with the appropriate work function to make injection of chargecarriers such as calcium, aluminum, gold, or silver.

The organic layers 104 can be implemented with any organicelectroluminescent material such as a light-emitting polymer, an exampleof which is described in U.S. Pat. No. 6,605,483, which is incorporatedherein by reference as if fully set forth. Other examples of suitablelight emitting materials include evaporated small molecule materials,light-emitting dendrimers, molecularly doped polymers, andlight-emitting electrochemical cells.

The light extraction film 116 in this embodiment is composed ofsubstrate 114, optional barrier layer 112, low index structure 110, andhigh index structure 108. The high index structure uses a backfillmedium to effectively provide a planarizing layer over the low indexstructure in order to make the light extraction film sufficiently planarto allow OLED fabrication. The backfill layer can alternatively haveother optical properties. Also, the backfill layer material can functionas a barrier to moisture and oxygen or provide electrical conduction,possibly in addition to having barrier properties, depending upon thetype of material used. The backfill layer can alternatively beimplemented with an optically clear adhesive, in which case theextraction film can be applied to top emitting OLED device, for example.A stabilization layer can optionally be coated on the device beforeapplying the backfill layer.

The low index structure 110 has a material with an index substantiallymatched to the underlying layer, typically the substrate. The low indexstructure 110 is composed of a nanostructured layer, which can have aperiodic, quasi-periodic, or random distribution or pattern of opticalnanostructures, including photonic crystal structures. It can includediscrete nanoparticles. The nanoparticles can be composed of organicmaterials or other materials, and they can have any particle shape. Thenanoparticles can alternatively be implemented with porous particles.The distribution of nanostructures can also have varying pitches andfeature size. At least a portion of the extraction elements ornanostructures are preferably in contact with the flexible substrate,and the extraction elements may have voids beneath them. The layer ofnanoparticles can be implemented with nanoparticles in a monolayer, witha layer having agglomerations of nanoparticles, or in a multi-layer.

In some embodiments, the addition of small SiO₂ nanoparticles tosuspensions of larger SiO₂ nanoparticles for low index structure 110 cansignificantly improve the uniformity of the larger nanoparticles incoatings made from the suspension. For example, low index structure 110can include the additional of 5 nm diameter SiO₂ nanoparticles incoatings made from suspensions of 440 nm diameter SiO₂ nanoparticles.These small and large nanoparticles can be surface treated ornon-treated. The large nanoparticles can comprises two or more differentsizes of large nanoparticles. The large nanoparticles preferably havediameters in the range of 60 nm to 10 microns, or 100 nm to 1 micron, ormore preferably 100 nm to 500 nm. The small nanoparticles preferablyhave diameters in the range of 3 nm to 50 nm. The nanoparticles cancomprise one or more of the following: metal oxide particles; organicpolymer particles; metal particles; or composite particles.

Using a distance of the nanostructures on the order of the evanescentwave from the organic layers can result in coupling of the evanescentwave to the nanostructures for extraction of additional light from thedevice. This coupling preferably occurs when the light extraction filmis adjacent to the light emitting region of the self-emissive lightsource. When the backfill layer has a lower index than the structuredlayer, then the backfill layer preferably has a thickness substantiallyequal to the extraction elements. When the backfill layer has a higherindex than the structured layer, then the backfill layer can be thickerthan the extraction elements provided it can still interact with theevanescent wave. In either case, the structured layer and backfill layerare preferably in sufficient proximity to the light output surface inorder to at least partially effect the extraction of light from thatsurface.

The nanostructured features in layer 110 can be fabricated using anyprinting techniques for replication of submicron features such as thefollowing: imprinting; embossing; nanoimprinting; thermal- orphoto-nanoimprint lithography; injection molding; or nanotransferprinting. Another technique for fabricating the extraction elements isdescribed in Example 18 in U.S. Pat. No. 6,217,984, which isincorporated herein by reference as if fully set forth.

The high index structure 108 is a high index material providing indexcontrast to the adjacent low index nanostructured layer and provides aneffective planarization layer to it. The index of refraction mismatchbetween nanostructured layer 110 and backfill medium 108 at the emissionwavelength(s) is referred to as Δn, and a greater value of Δn generallyprovides better light extraction. The value of Δn is preferably greaterthan or equal to 0.3, 0.4, 0.5, or 1.0. Any index mismatch between theextraction elements and backfill medium will provide for lightextraction; however, a greater mismatch tends to provide greater lightextraction and is thus preferred. Examples of suitable materials forbackfill medium 108 include the following: high index inorganicmaterials; high index organic materials; a nanoparticle filled polymermaterial; silicon nitride; polymers filled with high index inorganicmaterials; and high index conjugated polymers. Examples of high indexpolymers and monomers are described in C. Yang, et al., Chem. Mater. 7,1276 (1995), and R. Burzynski, et al., Polymer 31, 627 (1990) and U.S.Pat. No. 6,005,137, all of which are incorporated herein by reference asif fully set forth. Examples of polymers filled with high indexinorganic materials are described in U.S. Pat. No. 6,329,058, which isincorporated herein by reference as if fully set forth. The backfilllayer can be applied to form the planarizing layer using, for example,one of the following methods: liquid coating; vapor coating; powdercoating; or lamination.

Functionality can be added to the construction by depositing on it atransparent conductor such as ITO (n≈1.9-2.1) with high index, hightransparency and low sheet resistivity, to serve as the anode for theOLED device. The ITO can even be used as the backfill for the structure,if the layer can fill the structures and form into a smooth layerwithout adverse effects on the optical or electrical properties.Alternatively, after backfilling and smoothing, alternating metallic andorganic layers may be deposited to form a transparent conductiveoverlayer (on the backfill layer) in the manner as described in U.S.Patent Application Publication No. 2004/0033369, which is incorporatedherein by reference as if fully set forth.

Additional flexibility in the functionality of the extractor pattern ofthe photonic crystal structures or nanostructures can be obtainedthrough the use of photonic quasicrystal structures. These quasicrystalstructures are designed using tiling rules; they have neither trueperiodicity nor translation symmetry but have a quasi-periodicity withlong-range order and orientation symmetry, examples of which aredescribed in the following reference, which is incorporated herein byreference as if fully set forth: B. Zhang et al., “Effects of theArtificial Ga-Nitride/Air Periodic Nanostructures on Current InjectedGaN-Based Light Emitters,” Phys. Stat. Sol. (c) 2(7), 2858-61 (2005).The photonic quasicrystal structures offer the possibility of apseudogap for all propagation directions, and they exhibit unique lightscattering behaviors. In particular, these patterns of quasiphotoniccrystal structures can eliminate artifacts resulting from the regularityof conventional photonic crystal structures, and they can be used totailor unique light emission profiles and possibly can eliminateundesirable chromatic effects when working with broadband OLED emitters.Photonic crystal structures are described in the following patents, allof which are incorporated herein by reference as if fully set forth:U.S. Pat. Nos. 6,640,034; 6,901,194; 6,778,746; 6,888,994; 6,775,448;and 6,959,127.

Embodiments can involve the incorporation of the diffractive orscattering nanostructures into a film product which could becontinuously produced, for example, on a web line having a polymer filmor ultrabarrier coated film substrate fed to a 3C replication processfollowed by deposition of a high index backfill medium. Alternate waysto incorporate the diffractive or scattering nanoparticles into the filminclude solution coating a dispersion of particles. This film can bedesigned to be used directly as the substrate on which a bottom emittingOLED is fabricated, enabling the production of a film capable of manyuses in addition to enhancing light extraction.

Additional functionality could be incorporated into the light extractionfilm product by forming the extraction structures on an optionalultrabarrier film, which provides excellent moisture and oxygen barrierproperties. Ultrabarrier films include multilayer films made, forexample, by vacuum deposition of two inorganic dielectric materialssequentially in a multitude of layers on a glass or other suitablesubstrate, or alternating layers of inorganic materials and organicpolymers, as described in U.S. Pat. Nos. 5,440,446; 5,877,895; and6,010,751, all of which are incorporated herein by reference as if fullyset forth.

Materials may also be incorporated within the film to enhance lightextraction through scattering or to filter, color shift, or polarize thelight. Finally, surface coatings or structures, for example functionallayers 115, can be applied to the air surface of the light extractionfilm in order to further increase the functionality and possibly valueof a light extraction film. Such surface coatings can have, for example,optical, mechanical, chemical, or electrical functions. Examples of suchcoatings or structures include those having the following functions orproperties: antifog; antistatic; antiglare; antireflection; antiabrasion(scratch resistance); antismudge; hydrophobic; hydrophilic; adhesionpromotion; refractive elements; color filtering; ultraviolet (UV)filtering; spectral filtering; color shifting; color modification;polarization modification (linear or circular); light redirection;diffusion; or optical rotation. Other possible layers to be applied tothe air surface include a barrier layer or a transparent electricallyconductive material.

Top Emitting OLED Display Device

FIG. 2 illustrates a structure of top emitting OLED device 120 with afilm substrate having a light extraction film. Table 2 describes theexemplary elements of the device 120 and the arrangement of thoseelements, as identified by the reference numbers provided in FIG. 2.Each layer of the device can be coated on or otherwise applied to theunderlying layer. The configurations shown in FIGS. 1 and 2 are providedfor illustrative purposes only, and other configurations of bottomemitting and top emitting OLED display devices are possible.

TABLE 2 Top Emitting OLED Device with Light Extraction Film Ref. No.Type of Element 121 optional functional layers 122 substrate 1 124optional barrier layer 126 low index structure 128 high index structure130 optical coupling layer 132 electrode 1 134 optional thin filmencapsulant layer 136 organic layers 138 electrode 2 140 substrate 2 142light extraction film

The light extraction film 142 in this embodiment is composed ofsubstrate 122, optional barrier layer 124, low index structure 126, andhigh index structure 128. Low index structure 126 and high indexstructure 128 can be implemented with the exemplary materials andconstructions described above. Layers 128 and 130 can optionally beimplemented with a single layer. The substrates 122 and 140, optionalbarrier layer 124, electrodes 132 and 138, and organic layers 136 can beimplemented with the exemplary materials identified above. Substrate 140can also be optionally implemented with an opaque material such as ametal foil.

Optional thin film encapsulant 134 can be implemented with, for example,any suitable material for protecting the organic layers from moistureand oxygen. Examples of encapsulants for OLED devices are described inU.S. Pat. No. 5,952,778 and U.S. patent application Ser. No. 11/424,997,filed Jun. 19, 2006, both of which are incorporated herein by referenceas if fully set forth.

OLED devices, especially top emitting OLED devices as shown in FIG. 2,are optionally completed by depositing a thin film encapsulant,typically on a semitransparent electrode. This construction of an OLEDdevice provides an advantage; in particular it creates access to thecritical high index device-air interface after the completion of devicefabrication, enabling a lamination process for the application of thelight extraction film. For top emitting OLED devices, embodimentsinclude a light extraction film as described above for bottom emittingOLED devices. Alternatively, the film can be designed to be the cappinglayer on a top emitting OLED structure when combined with a suitablehigh index adhesive to serve as the optical layer 130 in order tooptically couple the OLED device to the light-extracting layer. Theencapsulant material may itself serve as the index contrast materialwhich backfills the nanostructures to form the light extraction layer.

OLED Solid State Lighting or Display Element

Top emitting OLED device 120 or bottom emitting OLED device 100 can alsobe used to implement an OLED solid state lighting or display element. Inaddition to the substrates identified above, examples of substratesuseful in top emitting OLED solid state lighting devices, includingflexible metal foils, are described in the following papers, all ofwhich are incorporated herein by reference as if fully set forth: D. U.Jin et al., “5.6-inch Flexible Full Color Top Emission AMOLED Display onStainless Steel Foil,” SID 06 DIGEST, pp. 1855-1857 (2006); and A.Chwang et al., “Full Color 100 dpi AMOLED Displays on Flexible StainlessSteel Substrates,” SID 06 DIGEST, pp. 1858-1861 (2006).

FIG. 3 is a diagram illustrating a device 220 having spatially modulatedOLED devices for use in solid state lighting devices. Device 220includes a substrate 222 supporting a plurality of OLED devices 223,224, 225, and 226, each of which may correspond with the structuresdescribed above with respect to bottom or top emitting OLED displaydevices. Each of the OLED devices 223-226 can be individually controlledas represented by lines 228 and 230, which would provide electricalconnections to the anodes and cathodes in devices 223-226. Device 220can include any number of OLED devices 223-226 with electricalconnections, and substrate 222 can be scaled to accommodate them. Theindividual control of devices 223-226, via connections 228 and 230, canprovide for spatial modulation of them such that they are individuallyor in groups lighted in a particular sequence or pattern. Device 220 canbe used in solid state light, for example, on a rigid or flexiblesubstrate 222.

OLED Backlight Unit

FIG. 4 is a diagram of a top emitting OLED backlight unit 180 with lightextraction film. Table 3 describes the exemplary elements of thebacklight unit 180 and the arrangement of those elements, as identifiedby the reference numbers provided in FIG. 4. Each layer of backlightunit 180 can be coated on or otherwise applied to the underlying layer.Alternatively, bottom emitting OLEDs can also be used for backlightunits.

TABLE 3 OLED Backlight Unit with Light Extraction Film Ref. No. Type ofElement 182 polarizer 184 optional prism layer 186 optional asymmetricreflective film 188 optional diffuser 189 substrate 1 190 low indexstructure 192 high index structure 194 optical coupling layer 195optional thin film encapsulant layer 197 electrode 1 200 organic layers202 electrode 2 204 substrate 2 206 auxiliary optical films 208 lightextraction film

The light extraction film 208 in this embodiment is composed of lowindex structure 190 and high index structure 192. The light extractionfilm can optionally also include prism layer 184 and diffuser 188. Lowindex structure 190 and high index structure 192 can be implemented withthe exemplary materials and constructions described above. The otherelements of this embodiment, as provided in Table 3, can be implementedwith the exemplary materials identified above. Layers 192 and 194 canalternatively be implemented with a single layer.

FIG. 5 is a diagram illustrating OLED devices used as a liquid crystaldisplay (LCD) backlight unit 242 for an LCD panel 240. Backlight unit242 may correspond with the structure 180. The backlight unit 242 canalternatively be implemented with the spatially modulated light panelshown in FIG. 3. LCD panel 240 typically includes the entire LCD deviceexcept the backlight and drive electronics. For example, LCD panel 240typically includes the backplane (subpixel electrodes), front and backplates, liquid crystal layer, color filter layer, polarizing filters,and possibly other types of films. Use of OLED devices as a backlightmay provide for a thin, low power backlight for LCDs. An example of LCDpanel components and a backlight unit are described in U.S. Pat. No.6,857,759, which is incorporated herein by reference as if fully setforth.

High Index/Low Index Regions and Surface Configurations

FIGS. 6-9 are diagrams depicting the possible spatial configurations ofextraction elements. FIG. 6 illustrates a low index structure 250,having a regular pattern of nanostructures, with a high index structure251 providing a planarizing layer over the nanostructures. Thestructures 250 and 251 are located between a low index substrate 246 andan OLED device region 247. FIG. 7 illustrates a low index structure 252,having an irregular pattern of nanostructures, with a high indexstructure 253 providing a planarizing layer over the nanostructures. Thestructures 252 and 253 are located between a low index substrate 248 andan OLED device region 249. In FIGS. 6 and 7, the low and high indexstructures are located between a substrate and an OLED device (lightemitting) region.

FIG. 8 illustrates high index extraction elements 255 within a low indexbackfill region 254 with the low index region 254 providing theplanarizing layer. The extraction elements 255 and backfill 254 arelocated between a low index substrate 260 and an OLED device region 259.FIG. 9 illustrates low index extraction elements 257 within a high indexbackfill region 256 with the high index region 256 providing theplanarizing layer. The extraction elements 257 and backfill 256 arelocated between a low index substrate 261 and an OLED device region 262.In the embodiments shown in FIGS. 8 and 9, the extraction elements areconcentrated in the evanescent zone. The layers shown in FIGS. 6-9illustrate patterns and interfaces of the low index and high indexstructures described above.

FIGS. 10-14 are top view diagrams depicting possible surfaceconfigurations of extraction elements. FIGS. 10 and 11 illustrateregular periodic arrays of extraction elements. FIG. 12 illustrates arandom distribution of extraction elements. FIG. 13 illustratespatterned regions of extraction elements. In particular, FIG. 13illustrates portions of features, possibly in a regular pattern 264 oran irregular pattern 265, interspersed within a different distributionof features 263. The regular or irregular patterns 264 and 265,respectively, along with the different distribution 263 may each haveperiodic, quasi-periodic, or random distributions of extractionelements. Such regions of patterns may be useful to optimize extractionof particular wavelengths of light at those regions, for examplewavelengths corresponding with red, green, and blue light. In that case,the extraction regions can correspond and be aligned the red, green, andblue regions comprising pixels of a display device, and each extractionregion can each be optimized to extract light from the correspondingred, green, and blue regions. FIG. 14 illustrates quasicrystal (tiledpatterns) of extraction elements.

Examples of techniques for making extraction elements are described inU.S. patent application Ser. No. 11/556,719, filed Nov. 6, 2006, whichis incorporated herein by reference as if fully set forth. FIGS. 10-14illustrate possible surface configurations of the nanostructures orother extraction elements described above with a backfill mediumproviding the planarizing layer over the nanostructures.

Additional techniques could include using lithography or interferencelithography to expose nanoscale regions in a photosensitive polymerdeposited on a flexible polymer web. After the exposure and developmentsteps, the remaining photosensitive polymer would then define ananostructured surface. Alternatively, this nanostructuredphotosensitive polymer surface can serve as an etch mask for exposure ofthe surface in an etching process. This etching technique would transferthe nanoscale pattern into the surface of the underlying polymer web orinto a layer of a harder material, such as a silicon oxide, which hadbeen deposited on the polymer web prior to the lithographic steps. Thenanoscale surface defined in any of these manners could then bebackfilled with an index contrasting medium to form the light scatteringor diffracting layer.

Distributions of Nanoparticles for Light Extraction

This embodiment provides enhanced light extraction from an OLED using anindex-contrasting film with randomly distributed high indexnanostructures created by coating nanoparticles such as, for example,ITO, silicon nitride (Si₃N₄, referred to here as SiN), CaO, Sb₂O₃, ATO,TiO₂, ZrO₂, Ta₂O₅, HfO₂, Nb₂O₃, MgO, ZnO, In₂O₃, Sn₂O₃, AlN, GaN, TiN,or any other high index materials on a substrate used in OLEDfabrication or encapsulation, and then applying a low index coating,such as SiO₂, Al₂O₃, DLG, DLC, or polymeric materials over thenanoparticles to provide the index contrast needed for scattering ordiffraction efficiency and to planarize the surface. The randomlydistributed nanostructures can be in contact with the substrate,proximate the substrate, grouped together in places, or in any randomconfiguration proximate the substrate. A converse construction,potentially providing similar effectiveness, can comprise a randomdistribution of low index nanoparticles or nanostructures such as SiO₂,porous SiO₂, Borosilicate (BK), Al₂O₃, MgF₂, CaF, LiF, DLG, DLC, metalparticles such as silver or gold particles, poly(methyl methacrylate)(PMMA), polycarbonate, PET, low index polymers, or any other low indexmaterials with a contrasting high index filler material such as vapordeposited Si₃N₄ or a solvent-coated particle-filled polymer or a highindex polymer. The substrate can optionally have one or more of thefollowing coatings: an antistatic coating; or an adhesion promotioncoating.

Coating processes such as dip coating, knife coating, dye coating, androll-to-roll coating may be used for distributing the nanoparticles onthe surface, and a similar process may be used to coat thebackfill/planarization layer. The use of such techniques should renderthe process simple, easily scaled for manufacturing, and suitable forincorporation in film products manufactured via web line or roll-to-rollprocesses.

The roll-to-roll continuous process fabrication of light extractionfilms can include assembling monolayer or sub-monolayer coatings of lowindex nanoparticles on a plastic substrate, the applying an overcoat ofhigh index material. An example of such a roll-to-roll process includescoating bare functionalized silica nanoparticles on plastic (PET)substrates and then overcoating those nanoparticles with a high indexbackfill material. The high index backfill materials can be obtained byloading epoxy or acrylate polymers with high index nanoparticles such asZrO₂ or TiO₂. Additional high index materials are described in U.S.patent application Ser. No. 12/262,393, filed Oct. 31, 2008, which isincorporated herein by reference as if fully set forth.

One particular manufacturing method involves applying nanoparticleshaving a first index of refraction onto a flexible substrate andovercoating a backfill layer on the nanoparticles to form a planarizinglayer over them. The backfill layer comprises a material having a secondindex of refraction different from the first index of refraction.Preferably, a substantial portion of the nanoparticles are within anevanescent zone adjacent to a light emitting region of a self-emissivelight source when the optical film is located against the self-emissivelight source. For example, a substantial portion of the nanoparticlescan be in contact with the substrate to be within the evanescent zone,although in some embodiments the substantial portion of thenanoparticles in the evanescent zone need not be in contact with thesubstrate.

Applying the nanoparticles can involve coating the nanoparticlesdispersed in a solvent onto the flexible substrate and allowing thesolvent to evaporate before overcoating the backfill layer. Applying thenanoparticles can also involve applying them in dry form to the flexiblesubstrate and then overcoating them with the backfill layer. Analternative to the method involves using substrate with a release agent,in which the particles are applied to a substrate with a release agent,the substrate with the particles is applied to a device substrate withthe particles in contact with it, and then the substrate is released totransfer the particles to the device substrate. On particular methodinvolves a single process to coat the substrate with nanoparticles, dryit, coat the backfill layer, dry it again, and then cure the resultingfilm. Yet another particular method involves a first process to coat thesubstrate with nanoparticles, dry it, and wind up the coating film, andthen a second process to unwind the film, coat the backfill layer, dryit again, and then cure the resulting film.

Replication Method

One solution for forming a master tool having nanostructures involvesthe use of interference lithography. Regular periodic features as smallas 100 nm-150 nm can be quickly written using this method. An advantageinvolves being able to write these patterns over larger areas, which canmake the process more amenable to manufacturing.

Production of a master tool for replication of the pattern can involvethe following. A substrate is coated with an overlayer of photoresistand then illuminated with one or more UV interference patterns to exposethe resist in a regular pattern with the desired feature sizes.Development of the resist then leaves an array of holes or posts. Thispattern can subsequently be transferred into the underlying substratethrough an etching process. If the substrate material is not suitable tobe used as a replication tool, a metal tool can be made using standardelectroforming processes. This metal replica would then become themaster tool.

Another method involves forming a master tool havingrandomly-distributed nanostructures. A solution is prepared comprisingnanoparticles of the appropriate size and with the appropriate surfacemodifications to prevent agglomeration. Methods for preparing suchsolutions are generally specific to the particular nanoparticles to bedispersed; general methods have been described elsewhere, including U.S.Pat. No. 6,936,100 and Molecular Crystals and Liquid Crystals, 444(2006) 247-255, both of which are incorporated herein by reference as iffully set forth. The solution is then coated onto a flexible substrateusing one of a variety of solvent coating techniques, including knifecoating, dip coating, spray coating, dye coating, or roll-to-rollcoating. Pretreatment of the substrate using methods such as plasmaetching may be required in order to assure uniformity of the solutioncoating. After solvent evaporation, the nanoparticles should bedistributed in a way that is microscopically random but macroscopicallyuniform. As was the case with the uniform tool fabrication processdescribed above, this pattern could then be transferred to an underlyingsubstrate material through an etching or embossing process, or a metaltool can be made using standard electroforming processes.

In any of these cases, if a flat master tool has been produced, it orits replicas may then be tiled together to form a larger tool, asdescribed in U.S. Pat. No. 6,322,652, incorporated herein by referenceas if fully set forth, or may be formed into a cylindrical tool forcompatibility with a roll-to-roll replication process.

Once a master tool has been produced, replication of the structure intoa polymer can be done using one of a variety of replication processes,including the 3C process. The substrate for this replication could beany polymer sheeting compatible with the chosen replication process; itmay be already coated with the ultrabarrier film as described above.Backfilling would then be performed downstream in, for example, achemical vapor deposition (CVD) or sputtering process which can deposita high index material, such as SiN or ITO, which is capable of fillingthe structures and then leveling out into a smooth layer. If SiN isused, this might then be followed by an ITO deposition process if aconductive upper layer is required. Alternatively, the downstreambackfilling may be performed in a solvent coating process using suitablematerials.

EXAMPLES Example 1 190 nm SiO₂ Nanoparticles with No 5 nm SiO₂Nanoparticles (Comparative Example)

Dispersions of spherical silica nanoparticles with nominal diameter of190 nm were obtained from the Nissan Chemical, 10777 Westheimer, Suite830, Houston, Tex. 77042, U.S.A. The nanoparticles were treated withpolyethylene oxide (PEO and dialyzed, 142971-86-4, 190 nm silica withPEO covered and dialyzed, 33.6% solids).

The process details of treated 190 nm SiO₂ nanoparticles with PEO are asfollows. 363 grams of Nissian MP-4540 (100 grams of silica) was added toa reaction vessel along with 7.5 grams of A1230 polyethylene oxidesilane from Momentive Performance Chemicals. The mixture was reacted for16 hours at 80° C. The reaction mixture was then dialyzed to remove anyunreacted silane and other impurities. The solution was place in a 2Spectra/Por Dialysis membrane having a MWCO (Molecular Weight Cut-Off)of 12-14,000. The material was dialyzed for 24 hours against constantlyflowing tap water.

The resulting nanoparticle suspension was diluted in 1 methoxy 2propanol to produce suspensions having 2 percent by weight solidscontent. The 190 nm SiO₂ nanoparticle solution was coated on a PETsubstrate by a dip coating (coating speed: 65 mm/min). It was shown fromSEM images that there was a de-wetting issue resulting in regions of thesubstrate having no particle coating.

Example 2 Improved Coating of 190 nm SiO₂ Nanoparticles Via Addition of5 Nm SiO₂ Nanoparticles (Treated)

A 2 wt % suspension of 190 nm SiO₂ nanoparticles was prepared asdescribed in Example 1, but with the addition of 1.1 wt % of 5 nm SiO₂(treated by PEO: 147426-45-01, 5 nm silica particles treated withSilquest A1230). The 190 nm SiO₂ nanoparticles were coated on a PETsubstrate by a dip coating (coating speed of 65 mm/min as in Example 1).Through comparison of SEM images from Example 1 and this sample, theuniformity of the coating was shown to have been improved by adding thesmall nanoparticles, although the de-wetting of the nanoparticlescoating had not completely disappeared.

Example 3 Improved Coatings of 190 nm SiO₂ Nanoparticles Via Addition ofUnmodified 5 nm SiO₂ Nanoparticles

A 2 wt % of 190 nm SiO₂ nanoparticles was prepared as described as inExample 1, but with the addition of 1.1 wt % of 5 nm SiO₂ (unmodifiedsmall 5 nm SiO₂ nanoparticles from Nalco Company, Nalco 2326). It wasclearly shown from SEM images that unmodified small SiO₂ nanoparticlescan significantly improve the large nanoparticle coating uniformity.

Example 4 190 nm SiO₂ Nanoparticles with 5 nm Modified SiO₂Nanoparticles (Modified with Isooctyltrimethoxysilane andMethyltrimethoxysilane)

A 2 wt % of 190 nm SiO₂ nanoparticles was prepared as described as inExample 1, but with the addition of 1.1 wt % of 5 nm SiO₂ nanoparticlesmodified with isooctyltrimethoxysilane and methylrimethoxysilane. (The 5nm nanoparticle powder was first dissolved in isopropanol to producesuspensions having 10 percent by weight solids content). As was shownthrough SEM images, the coating uniformity was improved, although thede-wet of the nanoparticles coating had not completely disappeared.

Example 5a 440 nm SiO₂ Nanoparticles Coated by Roll-to-Roll Processwithout Small Nanoparticles (Comparative Example for Example 5b)

Dispersions of spherical silica nanoparticles with nominal diameter of440 nm were obtained from the Nissan Chemical (Houston Office (ChemicalBusiness), 10777 Westheimer, Suite 830, Houston, Tex. 77042, U.S.A. Thenanoparticle solution was diluted in 1 methoxy 2 propanol to produce asuspension having 5 percent by weight solids content. The 440 nm SiO₂nanoparticles were coated on a corona-treated PET film (6-8 milthickness) by roll-to roll-process using a 5 mil coating gap (web speedof 10 fpm, ind. pump speed of 1.2 cc/min). The resulting coating wasfirst dried in air at room temperature, then subsequently further driedat 180° F.

Example 5b 440 nm SiO₂ Nanoparticles Coated by Roll-to-Roll Process withSmall Nanoparticles

2.5 wt % of 440 nm SiO₂ nanoparticles were prepared as in Example 5a,but then 1 wt % of modified 5 nm SiO₂ nanoparticles, prepared as in theExample 2, was added. The 440 nm SiO₂ nanoparticles were coated on thecorona-treated PET film using the same conditions as in Example 5a.

Materials for Examples 6 and 7

Materials used in the Examples included silica nanoparticles of 93 nmnominal diameter obtained from the Nalco company, anddodecylbenzenesulfonic sodium salt (DS-10) surfactant obtained fromAldrich. Using these materials with different coating conditions,close-packed monolayers of nanoparticles, or sparse discontinuouslayers, could be achieved.

Mono-Layers of Bare Silica Nanoparticles Coated Directly on a PETSubstrate for Examples 6 and 7

A silica nanoparticle dispersion produced by diluting a 2 wt %nanoparticles dispersion in H₂O to 1 wt % nanoparticles with DS-10 wascoated on a corona-treated PET film (6-8 mil thickness) by theroll-to-roll process using a 5 mil gap (web speed of 10 fpm, dispersiondelivery rate of 3 cc/min). The coating was dried in air at roomtemperature, and then subsequently it was further dried at 180° F. Itwas shown through a SEM photo of the resulting nanoparticle that auniform and close-packed monolayer of silica nanoparticles was produced.

Discontinuous Layer of Bare Silica Nanoparticles Coated Directly on PETSubstrate for Examples 6 and 7

Silica nanoparticle dispersion as above was coated on corona-treated PETfilm (6-8 mil thickness) by the roll-to-roll process with a 5 mil gapand lower dispersion delivery rate (web speed of 10 fpm, dispersiondelivery rate of 1.5 cc/min). The resulting coating was dried in air atroom temperature, and subsequently further dried at 180° F. on the web.

Example 6 Light-Extracting OLED Substrate with Silicon NitrideOvercoated Nanoparticles

In order to quantitatively evaluate the OLED efficiency enhancement dueto the nanoparticle, 300 nm Si₃N₄ layer was applied over the silicananoparticle coating using plasma-enhanced chemical vapor deposition(PECVD, Model PlasmaLab System100 available form Oxford Instruments,Yatton, UK). Conditions used in the Si₃N₄ deposition are shown in Table4.

TABLE 4 Conditions Used for Depositing S3iN4 Layer Reactant/ConditionValue SiH₄ 400 sccm NH₃ 20 sccm N₂ 600 sccm Pressure 650 mTorrTemperature 60° C. High frequency (HF) power 20 W Low frequency (LF)power 20 WThe refractive index of the Si₃N₄ overcoating was measured using aMetricon Model 2010 Prism Coupler and was found to be 1.7. At thecompletion of the PECVD process, a low index scattering center with highindex backfilling film had been generated.

Next, 110 nm of ITO was deposited on the silicon nitride through a 5mm×5 mm pixilated shadow mask to serve as the OLED anode. Subsequently,a simple green organic emitting layer and cathode were deposited tocomplete the OLED. The OLEDs were fabricated by standard thermaldeposition in a bell-jar vacuum system. The OLED layers were depositedthrough a 40 mm×40 mm shadow mask covering the 5 mm×5 mm ITO pixels inthe following order: TNATA:FeCl3 (3000A, 5%FeCl3)/NPD(400A)/Alq:C545T(300A, 2%)/Alq(200A)/7ALiF/Al.

The 5 mm×5 mm shadow mask was then realigned, and 250 nm of Al metal wasdeposited to form the cathodes contacting the tops of the pixels. Thisprocess provided OLED devices containing several independentlyaddressable 5 mm×5 mm pixels with 4 pixels disposed over nanoparticles.

Electroluminescence measurements showed enhanced OLED light extractionfrom the nanoparticle coated pixels. An improvement of 50% at currentdensities between 2-20 mA/cm² was shown with this modification.

Example 7 Light Extracting OLED Substrate having NanoparticlesOvercoated by High Index Polymer Applied in Roll-to-Roll Process

50-60 wt % of 10 nm ZrO₂ nanoparticles (refractive index of 1.85) weredispersed in acrylate to form a high refractive index (1.68) backfillpolymer (obtained from Brant U. Kolb, 145840-77-38F). This high indexpolymer was mixed with 1 methoxy 2 propanol (10 wt %) and was thencoated over the nanoparticles previously coated on PET by a roll-to-rollprocess with a 5 mil gap (web speed of 10 fpm, dispersion delivery rateof 1.6 cc/min). The resulting coating was dried in air at roomtemperature; subsequently, it was further dried at 180° F. on the web.The target thickness of the high index polymer was 300 nm; SEM imagesindicated an actual thickness of about 300 nm in excellent agreementwith the target thickness. The surface of the roll-to-roll coating wasshown to be very smooth compared with Si₃N₄ deposited by plasma enhancedchemical vapor deposition.

Example 8 93 nm SiO₂ Nanoparticles Coated by Roll-to-Roll Process with60 Nm SiN Overcoated on NPs as a Stabilization Layer Preparation ofNanopaticle Coating by Roll-to-Roll Process

Dispersions of 93 nm silica nanoparticles were obtained from the Nalcocompany. Polyvinyl alcohol (PVA, 98 mole % hydrolyzed, MW 78000) wasobtained from Polysciences, Inc., and was dissolved in water with 1 wt %solid content for the related experiments. Dodecylbenzenesulfonic sodiumsalt (DS-10) surfactant was obtained from Alderich.

A silica nanoparticle (NP) dispersion solution (93 nm, 1 wt %, 0.1-1 wt% DS-10) was coated on PET film (6-8 mil thickness) by a roll-to-rollprocess using a 5 mil gap (web speed of 10 fpm, dispersion delivery rateof 3 cc/min). The coating was dried in air at room temperature, and thensubsequently it was further dried at 180° F.

Preparation of 60 nm SiN Stabilization Layer by Plasma-Enhanced ChemicalVapor Deposition

The silica-nanoparticle-coated film was then over-coated with a 60 nmthick layer of silicon nitride by plasma-enhanced chemical vapordeposition (PECVD), for stabilization of the NPs (PECVD, ModelPlasmaLab™ System100 available form Oxford Instruments, Yatton, UK). Theparameters used in the PECVD process are described in Table 5.

TABLE 5 Conditions used for depositing SiN layer Reactant/Condition:Value: SiH₄ 400 sccm NH₃ 20 sccm N₂ 600 sccm Pressure 650 mTorrTemperature 100° C. High frequency (HF) power 20 W Low frequency (LF)power 20 WThe refractive index of the SiN core layer was measured using a MetriconModel 2010 Prism Coupler, and was found to be 1.7.

Preparation of High-RI Coating Using 50 nm TiO₂ and ZrO₂ Nanoparticles

In a glass jar, 4.5 g of ZrO₂ HIHC prepared as above, 6.78 g of 50 nmTiO₂ dispersion, 24.4 g of 2-butanone, 16.62 g of 1-methoxy-2-propanolwere mixed together. The mixture was stirred to form a homogenous whitecoating solution. The coating solution was applied on above sample (60nm SiN on 93 nm nanoparticles/PET) using spin-coating at 4000 rpm for 40seconds (Karl Suss spin coater, spin coater model CT62 fro SussMicroTec, Inc.), resulting in transparent high-index coatings. Thecoatings were cured using a Fusion UV-Systems Inc. Light-Hammer 6 UV(Gaithersburg, Md.) processor equipped with an H-bulb, operating undernitrogen atmosphere at 100% lamp power at a line speed of 30 feet/min (2pass). The thickness of the high-index coating was measured to beapproximately 150-200 nm. The refractive index of the high index coatingis measured as 1.85 using Metricon Prism Coupler.

At the completion of the TiO₂-polymer backfill coating, a lightextraction layer containing the low-index scattering nanostructureplanarized with the high-index backfill was produced.

Fabrication of OLED

Approximately 110 nm-thick ITO was deposited onto the backfill-coatedNPs structures through a 5 mm×5 mm pixilated shadow mask to define theanode geometry. Subsequently, a simple green organic emitting layer andcathode were deposited to complete the OLED. The OLEDs were fabricatedby standard thermal deposition in a vacuum system at base pressure ofca. 10⁻⁶ Torr. The following OLED construction was deposited: HIL(300nm)/HTL(40 nm)/EML(30 nm, 6%)/Alq(20 nm)/LiF(1 nm)/Al(200 nm). Aftercompletion, the OLED was encapsulated with 3M encapsulation barrier filmemploying SAES getter as a desiccant and oxygen scavenger in between theencapsulation film and the OLED cathode.

The 5 mm×5 mm shadow mask was then realigned, and 200 nm of Al metal wasdeposited to form the cathodes contacting the tops of the pixels. Thisprocess provided OLED devices containing several independentlyaddressable 5 mm×5 mm pixels with 4 pixels disposed over nanoparticles.

Electroluminescence measurements showed enhanced OLED light extractionfrom the nanoparticle coated pixels. An improvement of 50-100% was shownwith this modification.

1. A multifunctional optical film for enhancing light extraction from aself-emissive light source having a surface that outputs light,comprising: a flexible substrate substantially transmissive to lightemitted by the self-emissive light source; a structured layer ofextraction elements having a first index of refraction, wherein theextraction elements comprise nanoparticles disposed in a surface layermanner on the substrate, and the extraction elements form a non-planarsurface of the structured layer, and wherein the nanoparticles comprisefirst nanoparticles having diameters within a first range and secondnanoparticles added to the first nanoparticles and having diameters in asecond range less than and non-overlapping with the first range; abackfill layer comprising a material having a second index of refractiondifferent from the first index of refraction, wherein the backfill layerforms a planarizing layer over the nanoparticles on the non-planarsurface of the structured layer, forming a planar surface on a side ofthe backfill layer opposite the nanoparticles, wherein a substantialportion of the extraction elements are in optical communication with thelight output surface of the self-emissive light source when the planarsurface of the backfill layer is located against the light outputsurface of the self-emissive light source, wherein the structured layerand backfill layer are in sufficient proximity to the light outputsurface of the self-emissive light source when the planar surface of thebackfill layer is located against the light output surface of theself-emissive light source in order to at least partially enhance theextraction of light from the light output surface, and wherein the firstrange of diameters is 60 nm to 10 microns, and the second range ofdiameters is 3 nm to 40 nm; and a coating applied to the substrate andhaving at least one of the following functions: color filtering; colorshifting; polarization modification; antireflection; light redirection;diffusion; or optical rotation.
 2. A multifunctional optical film forenhancing light extraction from a self-emissive light source having asurface that outputs light, comprising: a flexible substratesubstantially transmissive to light emitted by the self-emissive lightsource; a structured layer of extraction elements having a first indexof refraction, wherein the extraction elements comprise nanoparticlesdisposed in a surface layer manner on the substrate, and the extractionelements form a non-planar surface of the structured layer, and whereinthe nanoparticles comprise first nanoparticles having diameters within afirst range and second nanoparticles added to the first nanoparticlesand having diameters in a second range less than and non-overlappingwith the first range; a backfill layer comprising a material having asecond index of refraction different from the first index of refraction,wherein the backfill layer forms a planarizing layer over thenanoparticles on the non-planar surface of the structured layer, forminga planar surface on a side of the backfill layer opposite thenanoparticles, wherein a substantial portion of the extraction elementsare in optical communication with the light output surface of theself-emissive light source when the planar surface of the backfill layeris located against the light output surface of the self-emissive lightsource, wherein the structured layer and backfill layer are insufficient proximity to the light output surface of the self-emissivelight source when the planar surface of the backfill layer is locatedagainst the light output surface of the self-emissive light source inorder to at least partially enhance the extraction of light from thelight output surface, and wherein the first range of diameters is 60 nmto 10 microns, and the second range of diameters is 3 nm to 40 nm; and acoating applied to the substrate and having at least one of thefollowing functions: antiabrasion; antismudge; hydrophobicity; orhydrophilicity.
 3. A multifunctional optical film for enhancing lightextraction from a self-emissive light source having a surface thatoutputs light, comprising: a flexible substrate substantiallytransmissive to light emitted by the self-emissive light source; astructured layer of extraction elements having a first index ofrefraction, wherein the extraction elements comprise nanoparticlesdisposed in a surface layer manner on the substrate, and the extractionelements form a non-planar surface of the structured layer, and whereinthe nanoparticles comprise first nanoparticles having diameters within afirst range and second nanoparticles added to the first nanoparticlesand having diameters in a second range less than and non-overlappingwith the first range; and a backfill layer comprising a material havinga second index of refraction different from the first index ofrefraction, wherein the backfill layer forms a planarizing layer overthe nanoparticles on the non-planar surface of the structured layer,forming a planar surface on a side of the backfill layer opposite thenanoparticles, wherein a substantial portion of the extraction elementsare in optical communication with the light output surface of theself-emissive light source when the planar surface of the backfill layeris located against the light output surface of the self-emissive lightsource, wherein the structured layer and backfill layer are insufficient proximity to the light output surface of the self-emissivelight source when the planar surface of the backfill layer is locatedagainst the light output surface of the self-emissive light source inorder to at least partially enhance the extraction of light from thelight output surface, wherein the first range of diameters is 60 nm to10 microns, and the second range of diameters is 3 nm to 40 nm, andwherein the substrate comprises one of the following: a polymer film; ora barrier material.
 4. A multifunctional optical film for enhancinglight extraction from a self-emissive light source having a surface thatoutputs light, comprising: a flexible substrate substantiallytransmissive to light emitted by the self-emissive light source; astructured layer of extraction elements having a first index ofrefraction, wherein the extraction elements comprise nanoparticlesdisposed in a surface layer manner on the substrate, and the extractionelements form a non-planar surface of the structured layer, and whereinthe nanoparticles comprise first nanoparticles having diameters within afirst range and second nanoparticles added to the first nanoparticlesand having diameters in a second range less than and non-overlappingwith the first range; and a backfill layer comprising a material havinga second index of refraction different from the first index ofrefraction, wherein the backfill layer forms a planarizing layer overthe nanoparticles on the non-planar surface of the structured layer,forming a planar surface on a side of the backfill layer opposite thenanoparticles, wherein a substantial portion of the extraction elementsare in optical communication with the light output surface of theself-emissive light source when the planar surface of the backfill layeris located against the light output surface of the self-emissive lightsource, wherein the structured layer and backfill layer are insufficient proximity to the light output surface of the self-emissivelight source when the planar surface of the backfill layer is locatedagainst the light output surface of the self-emissive light source inorder to at least partially enhance the extraction of light from thelight output surface, wherein the first range of diameters is 60 nm to10 microns, and the second range of diameters is 3 nm to 40 nm, andwherein the substrate has one or more of the following coatings: anantistatic coating; or an adhesion promotion coating.
 5. Amultifunctional optical film for enhancing light extraction from aself-emissive light source having a surface that outputs light,comprising: a flexible substrate substantially transmissive to lightemitted by the self-emissive light source; a structured layer ofextraction elements having a first index of refraction, wherein theextraction elements comprise nanoparticles disposed in a surface layermanner on the substrate, and the extraction elements form a non-planarsurface of the structured layer, and wherein the nanoparticles comprisefirst nanoparticles having diameters within a first range and secondnanoparticles added to the first nanoparticles and having diameters in asecond range less than and non-overlapping with the first range; and abackfill layer comprising a material having a second index of refractiondifferent from the first index of refraction, wherein the backfill layerforms a planarizing layer over the nanoparticles on the non-planarsurface of the structured layer, forming a planar surface on a side ofthe backfill layer opposite the nanoparticles, wherein a substantialportion of the extraction elements are in optical communication with thelight output surface of the self-emissive light source when the planarsurface of the backfill layer is located against the light outputsurface of the self-emissive light source, wherein the structured layerand backfill layer are in sufficient proximity to the light outputsurface of the self-emissive light source when the planar surface of thebackfill layer is located against the light output surface of theself-emissive light source in order to at least partially enhance theextraction of light from the light output surface, wherein the firstrange of diameters is 60 nm to 10 microns, and the second range ofdiameters is 3 nm to 40 nm, and wherein the nanoparticles consist of oneor more of the following: metal oxide particles; organic polymerparticles; metal particles; or composite particles.
 6. A multifunctionaloptical film for enhancing light extraction from a self-emissive lightsource having a surface that outputs light, comprising: a flexiblesubstrate substantially transmissive to light emitted by theself-emissive light source; a structured layer of extraction elementshaving a first index of refraction, wherein the extraction elementscomprise nanoparticles disposed in a surface layer manner on thesubstrate, and the extraction elements form a non-planar surface of thestructured layer, and wherein the nanoparticles comprise firstnanoparticles having diameters within a first range and secondnanoparticles added to the first nanoparticles and having diameters in asecond range less than and non-overlapping with the first range; abackfill layer comprising a material having a second index of refractiondifferent from the first index of refraction, wherein the backfill layerforms a planarizing layer over the nanoparticles on the non-planarsurface of the structured layer, forming a planar surface on a side ofthe backfill layer opposite the nanoparticles, wherein a substantialportion of the extraction elements are in optical communication with thelight output surface of the self-emissive light source when the planarsurface of the backfill layer is located against the light outputsurface of the self-emissive light source, wherein the structured layerand backfill layer are in sufficient proximity to the light outputsurface of the self-emissive light source when the planar surface of thebackfill layer is located against the light output surface of theself-emissive light source in order to at least partially enhance theextraction of light from the light output surface, and wherein the firstrange of diameters is 60 nm to 10 microns, and the second range ofdiameters is 3 nm to 40 nm; and a stabilization layer located betweenthe nanoparticles and the backfill layer.